If the skater takes full advantage of all pre-rotation and short rotation, just more than 1/4 turn in the air is correct for a toe loop (and a loop). Trevor Laak's website he was mantaining for awhile even walks through this, and he's a fairly well respected coach.

1. Skaters typically can pre-rotate up to 1/2 of a rotation before the toe pick leaves the ice completely.
2. There aren't any official rules for the take-off. It depends on the judge.
3. It's not considered bad form according to most judges I've spoken to.
4. I've never seen this specified in the rule-book. It's up to the judges whether or not they think it affects the GOE.